In a regulatory context favorable to non-synthetic refrigerant fluids, the aim of the project is to achieve proof of concept for a heat pump (HP) using natural, non-flammable and non-toxic fluids: water and CO2. The novel combination of these two abundant and inert fluids makes it possible to exploit the thermodynamic advantages of each while cancelling out their disadvantages. The use of water and CO2 stands out from the use of hydrocarbon and fluorinated refrigerants, which are respectively highly flammable and harmful to the environment. Laboratory tests in a simulated environment (climatic chamber and hot water network) will be used to validate the concept and create a data-driven model. This model will be used to carry out an energetic and environmental assessment of the solution for real-life use cases, simulated by building thermal models and a Life Cycle Assessment (LCA). The LCA can then highlight and help to improve this solution's comparative advantage over others in terms of environmental impact. The approach therefore involves several scales of analysis (from component to system) in order to correctly quantify the HP's performance, and is also cross-cutting as it focuses on technological innovation and environmental impacts, which we consider essential to guarantee the objectives of the European industry's ecological transition. The project will create the technical basis for a safe and efficient HP segment that will be robust against regulatory uncertainties.